Pediatric anesthesia week 1 Flashcards
What times are considered preterm, neonate, infant, and child?
Pre-Term – prior to 37 weeks gestational age
Neonate 1-28 days of life
Infant 28 days -1 year
Child >1 year
Most significant part of transition occurs
within the first _____ hours after birth
24-72
4 Adaptive Changes
Establish FRC
Convert Circulation
Recover from birth asphyxia
Maintain core temperature
Fetal Hgb shifts oxyhemoglobin dissociation curve to the RIGHT OR LEFT?
To the left
[Increased O2 loading in the lungs/placenta, decreased O2 unloading at tissues]
O2 transport is accomplished by ______ which totals ______%
O2 transport is accomplished by fetal Hgb which totals 70-90%
4 Weeks
primitive lung buds develop from foregut
16 Weeks
branching of bronchial tree complete to 28 divisions, no further formation of cartilaginous airways
24 Weeks
primitive alveoli (saccules) and type II cells present; surfactant detectable; survival possible with artificial ventilation
28-30 Weeks
capillary network surrounds saccules; unsupported survival
36-40 Weeks
true alveoli present, roughly 20 million at birth
Birth-3mon
PaO2 rises as R to L mechanical shunts close
To 6 yrs.
rapid increase in alveoli 350 million at age 6
Traditional view – ____, _____ and _____ of birth asphyxia stimulates chemoreceptors that produce gasping followed by rhythmic breathing
Traditional view – hypoxemia, hypercarbia and acidosis of birth asphyxia stimulates chemoreceptors that produce gasping followed by rhythmic breathing
What allows gas exchange?
Increase in PO2, Decrease in CO2, Decrease in Pulmonary Vascular Resistance
Current View – rhythmic breathing occurs with _____ of the umbilical cord and increasing O2 tensions from air breathing
Current View – rhythmic breathing occurs with clamping of the umbilical cord and increasing O2 tensions from air breathing
What is the primary event of the respiratory system transition?
INITIATION OF VENTILATION
Changes the alveoli from a fluid-filled to an air-filled state
Large surface tension forces are overcome by the small radius of the curvature of the diaphragm
Infant must generate high negative pressure,
-70 cm H2O, to inflate the lungs
Treu/false:
Neonate and infant lungs prone to collapse – weak elastic recoil, weak intercostal muscles, intra-thoracic airways collapse during exhalation
FRC of approx. ______ ml/kg is established to act as a buffer against cyclical alterations in PO2 and PCO2 between breaths
FRC of approx. 25-30ml/kg is established to act as a buffer against cyclical alterations in PO2 and PCO2 between breaths
Why don’t infants have lung collapse all of the time?
Infants terminate the expiratory phase of breathing before reaching their true FRC which results in intrinsic PEEP and a higher FRC. When anesthetized, however, this protective mechanism is abolished. The opposing tonic state of the intercostal muscles is ove-rridden and atelectasis occurs.
The moral of this story – PEEP of 5cm H2O can help maintain FRC/lung inflation in the neonate during anesthesia.
______ depresses the neonate’s response to CO2
Hypoxia depresses the neonate’s response to CO2
How donNewborns respond to hypercarbia?
by increasing ventilation
Initial hyperpneic response is abolished by:
hypothermia and low levels of anesthetic gases
True/False: Response to hypoxia is biphasic – initial hyperpnea followed by depression of respiration in about 2 min
True
Hypoxia causes PROFOUND _______ in babies
bradycardia
Respiratory pauses exceeding 20 sec. or those accompanied by bradycardia or cyanosis
Contributing Factors for Apnea of Infancy
Increased Work of Breathing = FATIGUE
Very compliant upper airway structures and ribcage which tend to collapse during inspiration
Inefficient diaphragmatic contraction
Only 25% of muscle fibers in diaphragm are Type I fatigue- resistant work horse fibers vs. adults are 55%
THEY ARE VERY CARTILAGINOUS..everything breaks down (ribcage…)
More Contributing Factors for Apnea of Infancy
Increased O2 consumption 6ml/kg
Decreased FRC (non-functional residual capacity)
Increased closing volume
Where does gas exchange occur?
In the placenta
Lungs require only nutrient flow ______% of cardiac output
5-10%
Fetal intracardiac and extracardiac shunts exist to:
minimize blood flow to the lungs while maximizing flow/O2 delivery to organ systems
Ductus Venosus
Foramen ovale
Ductus Arteriosus
Deoxygenated blood travels the descending aorta to the umbilical arteries to the placenta (very low resistance to flow)
Oxygenated blood returns via the?
umbilical vein (PO2 35 mm Hg)
Ductus venosus diverts approx. 50% of blood away from the?
liver into the IVC then to the RA
Summary
The foramen ovale, ductus arteriosus, and ductus venosus are the shunts needed for effective fetal circulation that must close after birth to allow effective newborn circulation
Increased SVR, decreased PVR – flow through FO and DA becomes left to right, the shunts close, and circulation becomes like that of an adult
Utero – pulmonary vascular resistance high, systemic vascular resistance low
Born – systemic vascular resistance high, pulmonary vascular resistance low, shunts functionally close
Persistent Pulmonary Hypertension of the Newborn (PPHN)
Persistence of fetal shunting beyond the normal transition period in the absence of a structural heart defect.
Because the shunts are not anatomically closed immediately after birth, certain clinical conditions may contribute to either the persistence of or a return to fetal circulation
HYPOXIA and ACIDOSIS
Increased PVR
Pulmonary hypertension
Decreased PBF
RAP > LAP
Increased ductal flow
This can open the foramen ovale
Signs and Symptoms of persistent pulmonary htn of the newborn
Marked cyanosis
Tachypnea
Acidosis
Right to left shunt across FO and DA = marked cyanosis
(right to left = cyanotic shunt)
Treatment of persistent pulmonary htn of the newborn
Hyperventilation – maintain alkalosis
Pulmonary vasodilators – prostaglandin
Minimal handling
Avoidance of stress
*ADEQUATE VENTILATION AND OXYGENATION IS KEY
fetal kidney
Low renal blood flow
Low glomerular filtration rate (GFR)
By ____ weeks all nephrons are developed, so a premature babe has incomplete renal development.
By 34 weeks all nephrons are developed, so a premature babe has incomplete renal development.
First few days of life urine
Urine osmolarity 700-800 mOsm/L
Creatinine 0.8-1.2mg/dl
True/false: the neonate will continue to excrete Na even in the presence of a severe Na deficit
True.
Immature neonatal tubules do not completely reabsorb NA under the stimulus of aldosterone
Result – the neonate will continue to excrete Na even in the presence of a severe Na deficit
The neonate is therefore considered an “obligate sodium loser”
Urine Na
Adult 5-10 mEq/L
Neonate 20-25 mEq/L
Why is this so important? Because the renin-angiotensin-aldosterone system is the primary compensatory mechanism for the reabsorption of the Na and H2O losses of plasma, blood, GI tract fluid, and third space fluid during surgery
Moral of this story – choose your IV fluid with this in mind. Neonates cannot completely conserve Na, so a baby will continue to produce dilute urine to the point of dehydration without adequate fluid replacement. This fluid must contain Na!!!!
What is the best maintenance fluid for a baby?
Maintenance fluid should contain glucose D5.2NS (Balanced Maintenance Fluid in a Baby)
Do babies need blood replaced sooner vs later if blood loss happens in the OR?
Yes!
Higher Hgb/Hct (35% lowest acceptable) because of high O2 demand with limited ability to increase CO
Increased blood volume per unit weight
Increased cardiac output per unit weight
90 ml/kg blood volume in term baby
100ml/kg blood volume in pre-term baby
Heat loss is governed by
Conduction – surface to surface, use warm blankets, bair hugger
Convection – surface to air currents, reduce air movement across body. Most OR’s for neonates kept at 80 degrees
Radiation – electromagnetic energy from the body to colder objects in the room (highest % of loss), use heat lamps and “french fry” lights
Evaporation – vaporization , cover exposed body cavities and humidify inspired gas
What is the major component of thermal regulation in neonates?
Non-shivering thermogenesis
Metabolism of brown fat:
Develops in the fetus b/t 26-30 weeks gestation
Comprises 2-6% of the neonate’s total body weight
Located in the mediastinum, b/t the scapulae, around the adrenals, in the axilla
Abundant vascular supply and rich innervation of the sympathetic nervous system
